Low offset vertical hall device and current spinning method

ABSTRACT

One embodiment of the present invention relates to a vertical Hall-effect device. The device includes at least two supply terminals arranged to supply electrical energy to the first Hall-effect region; and at least one Hall signal terminal arranged to provide a first Hall signal from the first Hall-effect region. The first Hall signal is indicative of a magnetic field which is parallel to the surface of the semiconductor substrate and which acts on the first Hall-effect region. One or more of the at least two supply terminals or one or more of the at least one Hall signal terminal comprises a force contact and a sense contact.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 13/488,709filed on Jun. 27, 2012, which claims priority to U.S. application Ser.No. 13/022,844 filed on Feb. 8, 2011 (U.S. Pat. No. 8,829,900 issued onSep. 9, 2014). The contents of both of these applications (applicationsSer. Nos. 13/488,709 and 13,022,844) are hereby incorporated byreference in their entirety.

BACKGROUND

Hall-effect devices are often used in sensor applications forcontactless sensing of magnetic fields. FIG. 1 shows a conventional Hallplate 100. The Hall plate 100 is operated by providing a predeterminedcurrent 104 along a first axis 106 between first and second supplyterminals S₁, S₂. According to the Hall principle (and Lorentz's righthand rule as shown by 108), the presence of a magnetic field B causespositively charged particles (e.g., holes 110) which are traveling withvelocity v during flow of current 104, to be “steered” or deflected inthe F direction along second axis 112, thereby inducing a voltagedifferential between Hall effect terminals H₁ and H₂. The amount of“steering” or deflection of these charged particles depends on themagnitude of the magnetic field B, such that the magnitude of voltagedifferential between H₁ and H₂ is proportional to the magnitude ofmagnetic field B. Hence, in the presence of predetermined current 104,measuring the voltage across Hall effect terminals H₁ and H₂ provides anaccurate measurement of the magnetic field B.

As will be appreciated in greater detail below, the present disclosurerelates to improved Hall-effect measurement techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an operating principle of a conventional Hall plate.

FIGS. 2-3 illustrate a vertical Hall-effect device that suffers fromsome shortcomings.

FIG. 4 illustrates an equivalent circuit of FIGS. 2-3, including contactresistances which lead to offset errors.

FIG. 5 illustrates an equivalent circuit for contact resistance ofHall-effect sensors in accordance with some embodiments.

FIG. 6 illustrates a top view of a vertical Hall-effect device inaccordance with some embodiments.

FIGS. 7A-7D illustrate a series of applied biases and measured currentsfor the vertical Hall-effect device of FIG. 6.

FIG. 8 illustrates a top view of a vertical Hall-effect device inaccordance with some embodiments.

FIGS. 9A-9D illustrate a series of applied biases and measured currentsfor the vertical Hall-effect device of FIG. 8.

FIG. 10 illustrates a top view of another vertical Hall-effect device inaccordance with some embodiments.

FIG. 11 illustrates an embodiment of a vertical Hall-effect devicedivided across two tubs, rather than a single tub.

FIGS. 12A-12B illustrate another embodiment of a vertical Hall-effectdevice divided across two tubs.

FIG. 13 illustrates another embodiment of a vertical Hall-effect devicedivided across two tubs.

FIG. 14 shows a feedback circuit in accordance with some embodiments.

FIG. 15 shows a differential feedback circuit in accordance with someembodiments.

FIGS. 16A-16C show a vertical Hall-effect device that makes use of FIG.15's differential feedback circuit.

FIG. 17 shows another embodiment of a vertical Hall effect device.

FIG. 18 shows another embodiment of a vertical Hall effect device.

FIG. 19 shows another embodiment of a vertical Hall effect device.

DETAILED DESCRIPTION

The present invention will now be described with reference to theattached drawing figures, wherein like reference numerals are used torefer to like elements throughout, and wherein the illustratedstructures and devices are not necessarily drawn to scale.

In contrast to FIG. 1, which explained the Hall-effect in the context ofa relatively flat Hall plate, the present disclosure deals with accuratemeasurement techniques for vertical Hall-effect devices. FIGS. 2 and 3show a perspective view and a cross-sectional view, respectively, for avertical Hall-effect device 200 that suffers from some shortcomings.Vertical Hall-effect device 200 includes a hall sensing region 202(e.g., lightly doped n- region), which is coupled to supply contacts S1,S2 and Hall signal contact H.

The vertical Hall-effect device 200 is operated in a “voltageinput−current output” mode. To this end, a voltage source 204 applies aninput voltage Vin across the supply contacts S1, S2. For example, supplycontact S1 can be held at Vin while supply contact S2 can be held atground. In accordance with Ohm's law (V=IR), this input voltage Vininduces a corresponding current flow between supply contacts S1, S2.

Assuming the Hall signal contact H is centered between the supplycontacts S1, S2 and assuming that there is a uniform resistance over theHall region 202, then the Hall signal contact H will experience avoltage of Vin/2 at zero magnetic field. Hence, if Hall signal contact Hwas held at Vin/2 in the presence of zero magnetic field, this wouldconstitute an equilibrium condition and no current would flow into theHall signal contact H.

In the presence of a non-zero magnetic field B, however, the case isslightly different. Now charged carriers in the flow of current are“steered” or deflected according to the right hand rule 108 in anattempt to raise or lower the potential on the Hall signal contact H.For example, consider the illustrated case where B-field is directed inthe negative x-direction and positively charged holes flow in thenegative y-direction, such that the holes experience a Hall force thatdrives the holes downward from substrate surface 209 in an attempt tolower potential on Hall signal contact H. If the Hall signal contact His still clamped to Vin/2, the charges “steered” by the Hall-effect areunable to raise or lower the potential at the Hall signal contact H.Therefore, a Hall current I_(Hall) will be injected into or sunk fromthe Hall signal contact H to maintain equilibrium, wherein amount ofHall current injected or sunk is proportional to the magnitude of themagnetic field B. Thus, the Hall current I_(Hall) on Hall signal contactH is indicative of the magnitude of the magnetic field B.

Referring to FIG. 3, one can see a cross-section of the verticalHall-effect sensor 200 taken along axis 106. First supply contact S1 isimplemented as a first well region 205 (e.g., n-well doped n) with oneor more contacts 206 (e.g., shallow doped source/drain n+). Hall signalcontact H is implemented as a second well region 207 (e.g., n-well dopedn) with one or more respective contacts 210 (e.g., shallow dopedsource/drain n+). Second supply contact S2 is implemented as a thirdwell region 212 (e.g., n-well doped n) with one or more contacts 214(e.g., doped n+). An isolation structure 215 surrounds Hall region 202.

Ignoring the Hall signal contact H for the moment, let's brieflyconsider the case where voltage Vin is applied to first supply contact51, and ground potential (0V) is applied to second supply contact S2.The voltage Vin is applied to a metal 1 wire 216, so current flows overthis wire, traverses contact plugs 218, flows into highly dopedsource-drain diffusion region 206 (n+), spreads out in n-well 205 (n,which is more lightly doped than n+source/drain regions but more highlydoped than n-Hall region 202), until it finally enters the n-Hall region202. The same sequence in reverse order happens at for the second supplycontact S2.

Unfortunately, the contact resistances of the metal 1 wire 216, thecontact plugs 218, the n+ source/drain 206 and nwell 205 cause a voltagedrop, such that the potential Vin does not actually reach theHall-region 202. Although these contact resistances are low, they maystill cause a voltage drop of a few millivolts which can be significantgiven the fact that Hall-region 202 typically has a small resistance.Further, in the presence of a zero magnetic field, asymmetries in thegeometry of the Hall device can lead to non-zero Hall-effect signals—socalled raw offsets. Current spinning schemes combine signals of severalspinning cycles, such that this total (combined) signal tends to have amuch smaller raw offset than the individual current signals. Thiscombined raw offset can be referred to as a residual offset.

The reason for this residual offset can be appreciated from FIG. 4,which shows an equivalent circuit diagram including the “true” Halldevice 202 (that is the part of the Hall device which is made only ofn-Hall region, where the Hall-effect predominantly develops), plusadditional contact resistances (r1, r2, rH). Because these contactresistances are not precisely known (and can vary somewhat over themanufacturing process and show mismatch even within one device), thesecontact resistances cause inaccuracies in the applied voltage potential.For example, consider a hypothetical case where a voltage bias of 5V isapplied between 51 and S2, and where the contact resistances r1 and r2are unknown to the user, but are each actually 10% of the resistance ofthe Hall region 202, for example. In such a situation, an user mightexpect that the full 5V bias is applied to the Hall region, but in fact,only 0.8*5V=4V (i.e., 80% of the full bias) is applied over the Hallregion, due to a 0.5V voltage drop over each contact resistance (r1,r2). Thus, the potential at the positive supply S1 of the Hall region202 is 4.5V (instead of 5V) and at the negative supply S2 of the Hallregion 202 is 0.5V (instead of 0V).

These inaccurate potentials lead to residual offset errors for spinningcurrent techniques, particularly if the device has an electricalnonlinearity, such as when the resistance level of the resistors r1 andr2 depends on the potential applied. For example, in the real world, theresistance value of r1 is ever-so-slightly larger if 5V is applied S1and is ever-so-slightly smaller if 4.5V is applied to S1. In the sameway, the resistance value of r2 is smaller when 0V is applied to S2,compared to when 0.5V is applied to S2. This leads to the residualoffset.

Therefore, it is desirable to apply well defined potentials to theresistors to avoid these residual offset errors. Unfortunately, however,the resistors in FIGS. 2-4 are not directly accessible because of thesmall contact resistances for each contact. To circumvent the unknownvoltage drop along these contact resistances, the invention splits eachcontact (e.g., supply contacts S1, S2 and Hall signal contact H fromFIGS. 2-3) into two parts—a force contact (F) used to carry current anda sense contact (S) used to measure a voltage potential that develops atthe ‘true’ Hall device in the active Hall region. These force-sensecontacts achieve well defined potentials at all resistors of theequivalent circuit diagram in all operating phases of the spinningcurrent scheme, thereby limiting or avoiding residual offset errors.

FIG. 6 shows an example of a vertical Hall-effect device 600 that makesuse of “split” contacts in accordance with some embodiments. Within ann-type tub conductive tub 602 (which is surrounded by an isolationstructure 606, such as a deep trench isolation region or a p-typeregion) three pairs of “split” contacts are arranged (e.g., firstcontact pair 610, second contact pair 612, third contact pair 614). Eachcontact pair includes a first contact (e.g., 610 a, 612 a, 614 a) aswell as a second contact (e.g., 610 b, 612 b, 614 b). As will beappreciated in more detail below, feedback circuits 626, 628, 630 clampthe contact pairs to respective voltage potentials (e.g., U1, U2, U3)and measure a Hall-effect current from the biased device to accuratelymeasure magnetic field.

Before delving into the detailed functionality of vertical Hall-effectdevice 600, reference is made to FIG. 14, which illustrates an exemplaryfeedback circuit 1400 (e.g., feedback circuit 626 in FIG. 6). Thefeedback circuit 1400 comprises a transconductance input stage TC₁ andCurrent Controlled Current Source CCCS₁. The transconductance inputstage TC₁ comprises a positive non-inverting input (+) and a negativeinverting input (−). The transconductance input stage TC₁ is configuredto output a current I_(TC) that is proportional to the voltage betweenits non-inverting (+) and inverting (−) inputs. If the voltage at thenon-inverting input is positive against the inverting input, the outputcurrent I_(TC) is positive. If the voltage at the non-inverting input isnegative against the inverting input, the output current I_(TC) isnegative.

The output current I_(TC) of the transconductance stage TC₁ is providedto CCCS₁, which outputs a feedback current I₁ to a force contact F₁ todrive the voltage potential at an associated sense contact to thereference voltage potential U₁ (e.g., feedback current I₁ is provided toF₁ to drives the voltage potentials at S₁ to be equal to U₁). If TC₁comprises a large factor of proportionality, a small voltage differencebetween the inverting inputs can provide a large output current toCCCS₁, since I₁ is proportional to current I_(TC) and is independent ofthe contact resistance to which the current is supplied. In order tosuppress the effect of contact resistances efficiently, the magnitude ofcurrent I1 must be much larger than the magnitude of the current flowingin or out of the inverting input of TC1. In an idealized case theinverting input draws no current at all.

Therefore, during operation, if the voltage potential at a sense contact(e.g., S₁) is lower than the reference or target voltage potential ofthe feedback circuit (e.g., U₁), the feedback circuit (e.g., FB₁)injects a large positive current (e.g., I₁) into a force contact (e.g.,F₁) of the Hall-effect device to raise the potential at the sensecontact (e.g., S₁) until it is equal to the reference voltage (e.g.,U₁). Similarly, if the voltage potential at a sense contact (e.g., S₁)is higher than the reference or target voltage potential of the feedbackcircuit (e.g., U₁), the feedback circuit (e.g., FB₁) reduces its outputcurrent supplied to a force contact (e.g., F₁) of the Hall-effectdevice, thereby lowering the potential at the sense contact (e.g., S₁)until it is equal to the reference voltage (e.g., U₁).

Referring now to FIGS. 7A-7D, one can see operation of the Hall-effectdevice 600. In FIG. 7A, at a first time, controller 624 sets switchingnetwork 636 to couple respective feedback circuits (626, 628, 630,respectively, having reference voltages +1V, +0.5V, and 0V,respectively) to contact pairs 610, 612, 614, respectively.

More particularly, in the illustrated example, the first feedbackcircuit 626 is coupled to first contact pair 610 for FIG. 7A. The firstfeedback circuit 626 changes the amount of current I1 delivered to forcecontact F1 until sense contact S1 measures a voltage of U1 (here 1V). Inthis way, first and second contacts 610 a, 610 b are clamped at 1Vduring first time in FIG. 7A. In this way, first contact 610 a isclamped at 1V. Similarly, second contact 612 a is clamped to 0.5V, andthird contact 614 a is clamped to 0V (612 b will have a potential closeto 0.5V, maybe slightly smaller or larger than 0.5V depending on itscontact resistance and applied magnetic field, whereas 614 b will have apotential slightly lower than 0V depending on its contact resistance).This voltage bias induces a current between force contact 610 b andforce contact 614 b (due to V=IR), and magnetic field B drives thecharged carriers of this induced current upward or downward with respectto the upper planar surface of substrate depending on the direction ofthe magnetic field B. Because the voltage potential on sense contact S2(612 a) is clamped at 0.5V and because feedback circuit FB2 does notallow current to be drawn into/from S2 (S2 is only used for voltagemeasurement), any Hall current I_(hall) will be sunk into or injectedfrom force contact F2 612 b depending on the direction and magnitude ofB. FB2 (or an ammeter elsewhere) can measure the Hall current injectedinto or sunk from F2 612 b, and thereby determine the correspondingmagnetic field.

In FIG. 7B, at a second time, the controller 624 changes the state ofthe switching network 636 to “flip” the currents/voltages for the firstand third contact pairs 610, 614 while leaving the second contact pair612 clamped at 0.5V (e.g., FB1 626 is coupled to F3/S3 614 and FB3 630is coupled to F1/S1 610). This “flip” causes a new current I_(Hall′) tobe sunk into or injected from F2. The new current I_(Hall′) is againproportional to the magnetic field B, but will flow in the oppositedirection of I_(Hall) because of the switched voltage bias. If thedevice were perfectly symmetrical, the currents measured in FIG. 7A and7B would completely cancel one another, but in reality, FIG. 7B's Hallcurrent I_(Hall′) differs slightly from FIG. 7A's Hall current I_(Hall)due to slight imperfections in the geometries of the device and othernon-linearities. Assuming that magnetic field B is constant between FIG.7A and FIG. 7B, taking the difference between I_(Hall) (FIG. 7A) andI_(Hall′) (FIG. 7B) provides a greatly reduced offset (as any errorsbetween the two contacts, due to manufacturing imperfections and thelike, tend to cancel each other). Thus, the magnetic field B is measuredwith greater precision.

FIG. 7C shows the Hall sensor 600 at a third time, wherein thecontroller 624 has changed the state of the switching network 636 suchthat the force contacts and sense contacts have been “flipped”. Thus,the upper row of contacts (e.g., first contacts 610 a, 612 a, 614 a) nowact as force contacts, and the lower row of contacts (e.g., secondcontacts 610 b, 612 b, 614 b) now act as sense contacts. FIG. 7D showsthe Hall sensors at a fourth time wherein the biases are flippedhorizontally. Again, because the offsets inherent in these measuredcurrents tend to cancel one another, by iteratively measuring thecurrents and subtracting them, the offset can be finely turned and themagnetic field can be measured with high accuracy.

It is also possible to start with a slight variation of FIG. 7A whereonly S2/F2 are flipped for a first clock phase, and in a second clockphase use a slight variation of FIG. 7B where S2/F2 are flipped. Ingeneral, the force/sense contacts can be changed in any permutation(e.g., checker board). While there are countless versions of thesepermutations, the important aspect is how to apply well definedpotentials to the Hall region and how to extract output current from theHall device, which is accomplishing using the “split” contacts andcorresponding feedback circuits.

Note that in other (slightly more complicated) cases, the controller canapply Vin to S1 and concurrently drive S2 to ground. In the absence ofmagnetic field, the potential at S3 is no longer Vin/2, because S3 isnot positioned halfway between the sense contacts S1, S2. The exactpotential at S3 depends on the geometry (lateral and vertical) of theHall-effect device features. The potential at S3 will be roughly at 0.3Vfor many kinds of devices, but can vary widely. To find the potential,it can be measured in an end-of-line test at zero B-field. Then thecontroller can be programmed to apply exactly this potential (e.g.,0.3V) to S3 during actual operation. Subsequently, during actualoperation, a magnetic field would again like to raise or lower thevoltage potential on sense contact S3. However, because S3 is clamped to0.3V for example, a current will be injected to or sunk from S3 instead,wherein the amount of current provided is proportional to B-field.

Regardless of the particular biasing sequencing applied, the respective“first” and “second” contacts in contact pairs 610, 612, 614 areswitched between acting as so-called “force contacts” (current flowsthrough them) and so-called “sense contacts” (no current flows throughthem and they are used to measure the potential). Thus, the terms “forcecontact” and “sense contact” may be interchangeable in this respect, ascurrents and voltages may be measured and/or injected/applied from thevarious contacts depending on the time involved.

Referring back to FIG. 6, one will note that the first contacts 610 a,612 a, 614 a are arranged along a first line 616 extending in parallelwith a first axis 618, while the second contacts 610 b, 612 b, 614 b arearranged along a second line 620 extending in parallel with the firstaxis 618. The first and second lines 616, 620 are spaced equally apartfrom the first axis 618 by a distance D1, such that the respective firstand second contacts are spaced symmetrically about opposite sides of thefirst axis 618. A second axis 622, which is perpendicular to the firstaxis 618, passes through second contact pair 612 such that the first andthird contact pairs 610, 614 are spaced equally apart from the secondaxis 622 by distance D2.

In some embodiments, each first and second contact has outer dimensionsthat can range from approximately 0.2 um on a side to approximately 10um on a side. Contacts can be square, rectangular, polygonal, or evenrounded geometries; and multiple vias and/or multiple contact plugs canbe coupled to each first or second contact (e.g., 610 a). For example,for an illustrated rectangular contact 610 a, a shorter side 632 couldhave a width of approximately 1 um to about 0.2 um, while a longer side634 could have a length of approximately 3 um to approximately 10 um.The length and width can depend on the depth of the Hall region. Forexample, relatively shallow hall region of approximately 1 um mightcorrespond to a length of approximately 3 um; while a deeper hall regionof approximately 5 um might correspond to a width of approximately 10um.

FIG. 5 illustrates a schematic depiction of a vertical Hall-effectdevice 500 having “split contacts”. Relative to FIG. 4's circuitdiagram, each supply contact S1, S2 in FIG. 5's Hall-effect device hasbeen split into two contacts—a force contact (F)and a sense contact (S).Similarly, the Hall-effect contact H has been split into a force contact(F) and a sense contact (S). Each force contact its own contactresistance (e.g., rF1) as does each sense contact (e.g., rS1), which areconnected to a corresponding feedback circuit (e.g., FB1). Duringoperation, the feedback circuit FB1 pushes current 11 into F1, causing acorresponding voltage drop over rF1. However, little or no current isdrawn into port S1 of FB1, such that little or no voltage drop occursover rS1. Therefore, the potential on S1 is an extremely accuraterepresentation of the potential at terminal Hall region terminal 202 a.Therefore, FB1 can adjust 11 until the potential at the Hall region 202is exactly the one we want, namely Vin, which helps provide extremelyaccurate magnetic field measurements.

As can be appreciated from FIG. 8, the present disclosure is not limitedto three contact pairs as previously discussed with regards to FIG. 6.Rather, the concept can be applied to any number of contact pairs. FIG.8 shows one such example with four contact pairs, although additionalcontact pairs could also be used. The contacts of the contact pairs areagain arranged on first and second lines 802, 804 that are spaced apartfrom a first axis 806, and are symmetrically arranged about a secondaxis 808 which is perpendicular to the first axis 806.

FIG. 9A-9D show one manner of successively applying biases (e.g.,currents and voltages) to the contact pairs of FIG. 8 in a manneranalogous to previously described FIGS. 7A-7D. In a first clock phase(FIG. 9A), respective feedback circuits (not shown) are coupled tocontact pairs F1-S1, F2-S2, F3-S3, F4-S4, respectively, to establishpotentials Vin, k1*Vin, 0V, and k2*Vin (with k1 preferable close to 0.5,yet it may range from 0.2 . . . 0.8; and k2 closer to 0V) on S1, S2, S3,S4, respectively. The difference of currents I2-I4 is proportional tothe B-field.

In a second clock phase (FIG. 9B), the respective feedback circuits arecoupled to contact pairs F1-S1, F2-S2, F3-S3, F4-S4, respectively toestablish potentials k*Vin, Vin, k*Vin, and 0V (with k preferable closeto 0.5, yet it may range from 0.2 . . . 0.8) on S1, S2, S3, S4,respectively. The difference of currents I1-I3 is proportional to theB-field. The combination I1-I3-(I2-I4) is proportional to B-field andhas greatly suppressed offset error.

In a third clock phase (FIG. 9C) the measurement performed in the firstclock phase is re-taken, albeit with the force-contacts andsense-contacts interchanged. The Hall signal is I2′-I4′, which isproportional to magnetic field.

In a fourth clock phase (FIG. 9D) the measurement performed in thesecond clock phase is re-taken, albeit with the force-contacts andsense-contacts interchanged. The Hall signal is I1′−I3′. The combination[I1−I3−(I2−I4)]+[(I1′−I3′)−(I2′−I4′)] is proportional to B-field andshows even smaller offset error than above.

This spinning current scheme can be further improved by swapping thepositive and negative supply terminals in all clock phases and repeatingthe measurements. For example, in a fifth clock phase (not shown), wecan swap the supply terminals relative the illustrated first clock phase(FIG. 9B), such that the difference of currents I2″−I4″ is proportionalto the B-field. If we, in a sixth clock phase, swap the supply terminalsrelative to the second clock phase (FIG. 9B) the difference of currentsI1″−I3″ is proportional to the B-field. If, in a seventh clock phase, weswap the supply terminals relative to the third clock phase (FIG. 9C)the difference of currents I2−−I4′″ is proportional to the B-field. If,in an eighth clock phase, we swap the supply terminals relatively to thefourth clock phase (FIG. 9D) the difference of currents I1′″−I3′″ isproportional to the B-field. Lastly, we computeI1−I2−I3+I4+I1′−I2′−I3′+14′−(I1″−I2″−I3″+14″+I1′″−I2′″−I3′″+I4′″), whichis proportional to B-field and shows even smaller offset error thanabove. Moreover, it is also possible to swap e.g. F2 with S2 and F4 withS4 in FIG. 9A: then not all force contacts are in a single row anymore—only the force contacts of the supply terminals are in a row withthe sense contacts of the Hall effect terminals (=signal terminals). Inprinciple it is also possible to additionally swap F1 with S1: thisgives an asymmetric arrangement of force and sense contacts that islikely not to provide very good residual offset, yet it may still givebetter results than prior art

FIG. 10 shows another embodiment of a vertical Hall-effect device 1000where the contacts have a slightly different configuration. Likeprevious embodiments, the Hall-effect device 1000 includes a conductivetub 602 having a first conductivity type (e.g., n-type) disposed in asemiconductor substrate 604, and surrounded by isolation structure 606.The illustrated Hall-effect device 1000 again includes a three contactpairs 610, 612, 614. In this example, the first and third contact pairs610, 614, however, are each split into two vertical contacts. Thevoltage biases applied to and currents measured from the variouscontacts can be flipped such that all contacts act as a force contact atone time and a sense contact at another time, as previously described inFIGS. 7A-7D. Although it is generally advantageous to have force andsense contacts of equal size, the force and sense contacts may alsodiffer in size (e.g. the force contact may be larger to have a smallervoltage drop—there is no voltage drop along the sense path, becauselittle or no current flows there), as shown by first contact pair 610and third contact pair 614.

FIG. 11 illustrates an embodiment of a vertical Hall-effect device 1100that includes two tubs, rather than a single tub. The Hall-effect deviceincludes a first tub 1102, which is surrounded by isolation structure1104, and has a first conductivity type and is disposed in asemiconductor substrate. A first group of contact pairs 1106 havingrespective first and second contacts 1108, 1110 are disposed in thefirst tub 1102. First contacts 1108 are arranged along a first line 1112and second contacts 1110 are arranged along a second line 1114, whereinthe first and second lines 1112, 1114 run in parallel with a first tubaxis 1116 arranged between the first and second lines 1112, 1114.

A second tub 1118, which is surrounded by isolation region 1120, has thefirst conductivity type and is disposed in the semiconductor substrate.A second group of contact pairs 1122, which include respective third andfourth contacts 1124, 1126, are disposed in the second tub 1118. Thethird contacts 1124 are arranged on a third line 1128 and fourthcontacts 1126 are arranged on a fourth line 1130, wherein the third andfourth lines 1128, 1130 run in parallel with a second tub axis 1132arranged between the third and fourth lines. The tubs are notnecessarily parallel, but can also be orthogonal or at any angle.

An interconnect layer 1134 couples a first contact pair F1/S1 in thefirst tub 1104 with a second contact pair F6/S6 in the second tub 1118.The first and second contact pairs are spaced symmetrically about anaxis 1136 passing between the first and second tubs. The first andsecond contact pairs are also spaced symmetrically with respect to asecond axis that is perpendicular to the axis passing between the firstand second tubs. For example, the interconnect structure couples F1 toF6 and S1 to S6, all of which are driven by FB1. The interconnectstructure also couples F3 to F4 and S3 to S4, all of which are driven byFB2. Alternatively one may swap S4 with F4 and/or S5 with S5 and/or S6with F6. This gives a large number of possible configurations whereofthe preferred ones are those with higher degree of geometrical, thermal,electrical, and/or magnetic symmetry and/or symmetry with respect tomechanical stress on the devices.

Another Hall-effect sensor is illustrated in FIG. 12A-12B, wherein theHall-effect sensor 1200 is divided across two tubs. Hall-effect sensor1200 consists of two separate Hall regions, each one with threecontacts, where the center contacts of both tubs (C2, C5) are shorted.One of the other two contacts is used as a supply terminal and the otheras a Hall-effect signal terminal.

As shown in FIG. 12A in a 1^(st) clock phase, a positive supply voltageis applied to S1, and negative supply voltage is applied to S4. S3 andS6 are clamped to intermediate potentials and the difference I3−I6increases with increasing By-field.

Note that at vanishing magnetic field, I3−I6 is usually not equal tozero: this is the systematic raw offset of the device.

In a second clock phase, S3 is forced to the positive supply voltage andS6 to the negative one. Then S1 and S4 are forced to intermediatepotentials: ideally S1 is forced to the same potential as S3 was forcedin the 1^(st) clock cycle and S6 is forced to the same potential as S4was forced in the 1^(st) clock cycle. The difference I4−I1 increaseswith increasing By-field, and its systematic raw offset is equal inmagnitude and opposite in sign to the raw offset of clock phase 1.

A total signal I3−I6+I4−I1 has greatly reduced offset and largesensitivity to By-field.

Another two clock cycles #3 and #4 may be added, where the roles ofpositive and negative supply voltages are exchanged: this changes thesign of the respective signals I3′−I6′ and I4′−I1′ so that they have tobe subtracted from I3−I6+I4−I1−(I3′−I6′+I4′−I1′). This gives in total 4clock phases.

Another 4 clock phases #5, #6, #7, #8 may be added, where the roles offorce and sense contacts are exchanged, as shown in FIG. 12B.

In the clock phase #5 positive supply voltage is established on S1 a, S1b and negative supply voltage on S4 a, S4 b and intermediate voltagesare established on S3 a, S3 b and S6 a, S6 b. Then the currentdifference I3″−I6″ is measured.

In the clock phase #6 positive supply voltage is established on S3 a, S3b and negative supply voltage on S6 a, S6 b and intermediate voltagesare established on S1 a, S1 b and S4 a, S4 b. Then the currentdifference I4″−I1″ is measured.

In the clock phase #7 positive supply voltage is established on S4 a, S4b and negative supply voltage on S1 a, S1 b and intermediate voltagesare established on S3 a, S3 b and S6 a, S6 b. Then the currentdifference I6′″−I3′″ is measured.

In the clock phase #8 positive supply voltage is established on S6 a, S6b and negative supply voltage on S3 a, S3 b and intermediate voltagesare established on S1 a, S1 b and S4 a, S4 b. Then the currentdifference I1′″−I4′″ is measured.

The overall signal is computed:I3−I6+14−I1−(13′−I6′+14′−I1′)+I3″−I6″+I4″−I1″−(I3′″−I6′″+I4′″−I1′″). Ithas very small residual offset error and strong sensitivity to magneticfield.

A drawback of the device is the large raw offset due to the systematicdifference in potentials of both Hall-effect terminals in both tubs.

To reduce this large raw offset the tubs and contacts can be arrangedmore symmetrically as shown in FIG. 13. FIG. 13 illustrates anembodiment of a vertical Hall-effect device divided across four tubs1302, 1304, 1306, 1308. The wiring of individual contacts is such thattwo sense contacts (e.g. S3 and S7) and multiple force contacts (F3 a,F3 b, F7 a, F7 b) are coupled to each feedback circuit (e.g., FB3). Forthe sense contacts coupled to a given feedback circuit (e.g., which canbe accomplished via a switching network (not shown)), one of them isplaced in a tub with positive supply terminal (e.g. S3 if F1 is thepositive supply) and the other one is placed in a tub with negativesupply terminal (e.g. S7 if F9 is the negative supply). If these twosense contacts are shorted (i.e. their respective force-contacts F3 a,F3 b, F7 a, F7 b are shorted and also their respective sense contactsS3, S7 are shorted) a large difference current flows across these shortsin the absence of magnetic fields: this current corresponds to the rawoffset of devices. This short pulls down the potential in S3 and up inS7 so that finally they are both at half of the supply voltage of thevertical Hall device. Then the feedback circuit FB3 only has to supply asmall current I3 to the force contacts F3 a, F3 b, F7 a, F7 b to accountfor statistical offset (=mismatch between the devices) and to theapplied By-field.

Note that the above figure is a circuit diagram where only each tub withits contacts corresponds to the layout—it does not say anything aboutthe orientation of the four tubs in the layout. In a real layout thefour tubs may be aligned in a row on a single horizontal line, they maybe aligned in a column on a single vertical line, or they may be alignedin a quadrangle (e.g., 2×2 matrix).

Note that in FIG. 13 we may also skip two tubs in order to simplify thedevice. FIG. 11 illustrated one such example. In this instance, thepotentials are forced in such a way that the current flow in both tubsis in opposite directions: In the 1^(st) clock phase FB1 forces S1=S6=+1V and S3=S4=0V and S2=S5=0.5V. Then the difference in currents I2−I5 isproportional to the magnetic field. In a 2^(nd) clock phase FBI stillforces S1=S6=+1V, yet this time FB3 forces 0.5V (or some value between0.2V and 0.7V) on S3 and S4 and FB2 and FB5 force S2=S5=0V. Then thedifference in currents goes toward zero.

In some embodiments, a differential feedback circuit can be used, suchas shown in FIG. 15. Differential feedback circuit 1500 has two voltageinputs U1, U2 and two current outputs I1, I2 and two reference voltagesUd, Ucm and it controls I1 and I2 in such a way that U1−U2=Ud and(U1+U2)/2=Ucm. The control loop might look like this, however, there aremany modifications possible. The circuit subtracts U1—U2. Atransconductance amplifier TCd with high open loop gain compares thisvalue with Ud. If U1−U2>Ud then TCd outputs a large current into thecurrent controlled current source CCCSd, which also outputs a largecurrent (symbolized by the arrow at the upper end of the CCCSd symbol).The circuit also computes the average of U1 and U2 (=(U1+U2)/2) and TCcmcompares it with Ucm. If (U1+U2)/2>Ucm then TCcm outputs a large currentinto both current controlled current sources CCCSm, which output a largecurrent. The wiring ensures that I1=I(CCCScm)+I(CCCSd) andI2=I(CCCScm)−I(CCCSd). As shortcut: if Ud=0V or Ucm=0V we simply skip itin the symbol.

FIGS. 16A-16C show one example of how the differential feedback circuit1500 can be used. In a 1^(st) clock phase illustrated in FIG. 16A, dFB1forces the potential Usup on S1 and S6 and dFB2 forces 0V (=ground) onS3 and S4. dFB3 forces k*Usup on S2 and S5, with k=0 . . . 1 (preferably0.5). The current flows in the upper device from F1 to F3 and in thelower device from F6 to F4. Thus the current passes underneath F2 and F5in opposite directions. Therefore if F2 and F5 would be floating aBy-field would cause the potential at F2 to decrease and the potentialat F5 to increase. In the absence of magnetic fields the potentials atF2 and F5 would be at Usup/2, if the devices are symmetric. Usually theyare not symmetric, because the thickness of the depletion layer at theboundary of the device depends on the reverse bias voltage, which is afunction of the spatial coordinate. Therefore even in the case ofvanishing fields and perfect geometric symmetry of all tubs thepotential at F2 and F5 is not exactly 0.5*Usup but rather 0.4*Usup. Thisis why we may use the k-factor to account for this.

Note that instead of 0V (=ground) it may be advantageous to force aslightly higher potential (e.g. 0.2 . . . 0.5V) on S3, S4, because thisrequires even lower potential at F3, F4 and in most systems voltagesbelow 0V are not available. If we denote the positive supply voltage byVsupp and the negative one by Vsupn, then the Hall effect terminalsshould be forced at Vsupn+k*(Vsupp−Vsupn)/2: e.g. Vsupp=1V, Vsupn=0.25V,k=0.45. The output signal is I2′−I5′.

In the 2^(nd) clock phase (FIG. 16B) the only difference to the 1^(st)clock phase is that Ucm of dFB3 and dFB2 are swapped. The output signalis I3′−I4′.

In the 3^(rd) clock phase (FIG. 16C) the only difference to the 2^(nd)clock phase is that Ucm of dFB1 and dFB2 are swapped. The output signalis I1′−I6′. Note that in all 3 clock phases there is no systematic rawoffset (which means that at zero magnetic field and if there is nostatistic mismatch between the two Hall regions and its contacts theoutput signals vanish at each clock phase). Alternatively F2 and S2 canbe swapped as well as F5 and S5.

Although several examples have been shown above where the feedbackcontrol circuits establish respective predetermined reference potentials(e.g., U1, U2, U3=1 V, 0.5V, 0V, respectively in FIG. 7A), it will beappreciated that it is not necessary that the reference potential bepredetermined. In other embodiments discussed below with regards toFIGS. 17-19, the reference potential can correspond to a dynamicpotential on a sense contact, for example.

FIG. 17 shows a 5-contact device including force and sense contacts inaccordance with some embodiments. A lower row of sense contacts S1, S2,S3, S4, S5, and an upper row of force contacts F1, F2, F3, F4, F5 areshown. For purposes of simplicity a switching network is not shown,although the force contacts and sense contacts can be swapped, forexample as described in previous embodiments. Feedback circuits FB2 andFB3 are the same as in FIG. 14, and the feedback circuit FB1 is thesame, except the lower current terminal is now connected to F4 ratherthan ground.

In this arrangement, S3 is clamped to a predetermined referencepotential of +1.5V; while S1 and S5 are clamped to a predeterminedreference potential of +0.5V, such that current flows into F3.Approximately half of the current into F3 flows from F3 in an arc shapebelow F2 into F1; while the other half of the current into F3 flows fromF3 below F4 to F5. Rather than feedback circuit FB1 forcing a commonmode potential at S2 and S4, feedback circuit FB1 forces the differencein potentials S2−S4 to be zero (or some other predetermined value).Hence, unlike previous embodiments, the feedback circuit FB1 worksdifferentially between contacts 2 and 4. That is, FB1 senses thepotential difference between S2 and S4 and injects a current into F2while extracting the same current out of F4 so that S2−S4 is zero volts(or some other predetermined value). The current may also have oppositesign so that current is extracted out of F2 and injected into F4,depending on the process deviations and magnetic field applied. Becausesense contacts S2 and S4 (rather than predetermined reference voltagesfrom dedicated reference circuits) are used to provide referencepotentials to FB1, it will be appreciated that feedback circuits can usedynamic reference potentials rather than predetermined potentials.

In FIG. 18, feedback circuits FB3A and FB3B force the voltage between S2and S4 to zero. FB3A, FB3B each sense the voltage between S2 and S4—butonly block FB3A forces current to or from F4 (but not into or from F2)and only block FB3B forces current into or from F2 (but not into or fromF4). Notably, the reference potential of FB3A is the potential measuredat S2, which is not predetermined and which can vary dynamically. Thus,rather than the reference voltage used for the feedback circuits being apredetermined reference voltage supplied by a dedicated referencecircuit (e.g., a band−gap reference circuit or voltage divider)providing U1 to FB1 in FIG. 6, the reference potential may also besupplied by the Hall device itself (e.g., from a sense contact).

In FIG. 19, FB1 clamps the sense contact S3 to predetermined potentialof 1.5V and FB2 clamps S1 and S5 to 0.5V. A differential feedbackcircuit dFB3 is used to force S2−S4 to a predetermined differentialpotential U_(d) of zero volts and to force (S2+S4)/2 to a predeterminedcommon mode potential U_(CM) of +1 V. ((S2+S4)/2 is the common modepotential of S2, S4). Thus, FIG. 19's circuit forces not only thedifference but also the common mode, whereas FIGS. 17-18 force only thedifference voltage. Another aspect of FIG. 19 is that it shows how touse differential feedback circuits with a Hall device that has only asingle tub. In comparison, FIGS. 16A-16C disclosed how to usedifferential feedback circuits with two-tub devices.

Although the invention has been illustrated and described with respectto one or more implementations, alterations and/or modifications may bemade to the illustrated examples without departing from the spirit andscope of the appended claims. In particular regard to the variousfunctions performed by the above described components or structures(assemblies, devices, circuits, systems, etc.), the terms (including areference to a “means”) used to describe such components are intended tocorrespond, unless otherwise indicated, to any component or structurewhich performs the specified function of the described component (e.g.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary implementations of the invention. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“including”, “includes”, “having”, “has”, “with”, or variants thereofare used in either the detailed description and the claims, such termsare intended to be inclusive in a manner similar to the term“comprising”.

What is claimed is:
 1. A vertical Hall-effect device, comprising: aconductive tub having a first conductivity type and disposed in asemiconductor substrate; an isolation structure arranged around aperimeter of the tub to electrically isolate the tub from othersemiconductor devices that are outside the perimeter; a plurality ofcontact pairs having respective first and second contacts in the tub,wherein the respective first contacts are arranged along a first line inparallel with a first axis and wherein the respective second contactsare arranged along a second line in parallel with the first axis,wherein first and second lines are spaced apart from one another suchthat the respective first and second contacts are spaced symmetricallyabout the first axis; and a controller configured to, at a first time,concurrently apply a first potential to a force contact of a firstcontact pair, apply a second potential to a force contact of a secondcontact pair, and apply a third potential to a force contact of a thirdcontact pair; the controller further configured to measure a Hall effectcurrent from a sense contact of the first, second, or third contactpair; while the first, second, and third potentials are applied.
 2. Thevertical Hall-effect device of claim 1, wherein the first, second, andthird potentials are different.
 3. The vertical Hall-effect device ofclaim 1, further comprising a feedback circuit coupled to the firstcontact pair, and configured to control the first potential at a sensecontact of the first contact pair by providing one or more feedbacksignals to the force contact of the first contact pair.
 4. The verticalHall-effect device of claim 3, wherein the feedback circuit comprises: atransconductance input stage having a first input node configured toreceive an input signal from the sense contact, a second input nodeconfigured to receive a reference signal, and an output node configuredto output a current proportional to a voltage difference between thefirst and second input nodes; and a current controlled current sourceconfigured to receive the current from the output node and to generate afeedback current based thereupon that is provided to the force contactof the first contact pair.
 5. The vertical Hall-effect device of claim1, where the vertical Hall-effect sensor is operated in a spinningcurrent scheme that repetitively swaps how the first, second, and thirdpotentials are applied with respect to the first, second, and thirdcontacts, respectively, during operation.
 6. The vertical Hall-effectdevice of claim 1, where the measured Hall effect current corresponds toa magnetic field experienced by the Hall-effect device while the first,second, and third potentials are applied.
 7. The vertical Hall-effectdevice of claim 6, wherein the controller is adapted to, at a secondtime, concurrently apply the first potential to the force contact of thethird contact pair, the second potential to the force contact of thesecond contact pair, and the third potential to the force contact of thefirst contact pair.
 8. The vertical Hall-effect device of claim 7,wherein the controller is configured to measure a second Hall effectcurrent from a sense contact while the first, second, and thirdpotentials are applied during the second time.
 9. The verticalHall-effect device of claim 1, further comprising: a third contactarranged on the axis and spaced apart from the respective first contactsand the respective second contacts.
 10. The vertical Hall-effect deviceof claim 9, wherein the respective first contacts and the respectivesecond contacts are the same size and geometry as one another, andwherein the third contact is larger than a first contact and is largerthan a second contact.
 11. The vertical Hall-effect device of claim 1,wherein the conductive tub is an n-type region and the plurality ofcontact pairs are n-type regions.
 12. A vertical Hall-effect device,comprising: a first tub having a first conductivity type and disposed ina semiconductor substrate; a first plurality of contact pairs havingrespective first and second contacts in the first tub, wherein the firstplurality of contact pairs are collectively arranged along a first linein parallel with a first axis, wherein first and second contacts in acontact pair of the first plurality of contact pairs are spaced apartfrom one another so as to be symmetrically balanced about the firstline; a second tub having the first conductivity type and disposed inthe semiconductor substrate; a second plurality of contact pairs havingrespective third and fourth contacts in the second tub, wherein thesecond plurality of contact pairs are collectively arranged along asecond line in parallel with the first axis, wherein third and fourthcontacts in a contact pair of the second plurality of contact pairs arespaced apart from one another so as to be symmetrically balanced aboutthe second line; and an interconnect layer that couples a contact pairin the first tub with a contact pair in the second tub.
 13. The verticalHall effect device of claim 12, further comprising: a controllerconfigured to, at a first time, concurrently apply a first potential toa first contact of a first contact pair, apply a second potential to afirst contact of a second contact pair, and apply a third potential to afirst contact of a third contact pair, the controller further configuredto measure a Hall effect current from a second contact while the first,second, and third potentials are applied.
 14. The vertical Hall-effectdevice of claim 13, where the first contact of the second contact pairis arranged between the first and third contact pairs.
 15. The verticalHall-effect device of claim 14, wherein the second potential liesbetween the first and third potentials.
 16. The vertical Hall-effectdevice of claim 12, further comprising a feedback circuit coupled to theinterconnect layer, and configured to control a potential at sensecontacts of the contact pairs in the first and second tubs,respectively, by providing one or more feedback signals to forcecontacts of the contact pairs in the first and second tubs.
 17. Thevertical Hall-effect device of claim 16, wherein the feedback circuitcomprises: a transconductance input stage having a first input nodeconfigured to receive an input signal from a sense contact of a firstcontact pair, a second input node configured to receive a referencesignal, and an output node configured to output a current proportionalto a voltage difference between the first and second input nodes; and acurrent controlled current source configured to receive the current fromthe output node and to generate a feedback current based thereupon thatis provided to a force contact of the first contact pair.
 18. Thevertical Hall-effect device of claim 12, further comprising: a thirdcontact arranged on the axis and spaced apart from the respective firstcontacts and the respective second contacts.
 19. The verticalHall-effect device of claim 18, wherein the plurality of first contactsare spaced apart from one another on the first line and collectivelyspan a first total length along the first line, and wherein the thirdcontact extends continuously over the first total length on the thirdline.
 20. The vertical Hall-effect device of claim 12, wherein the firstand second conductive tubs are n-type regions and the first plurality ofcontact pairs and the second plurality of contact pairs are n-typeregions.